Electroacoustic binaural listening system



pril 25, 1950 H. c. SILENT 2,505,535'

ELECTROACOUSTIC .BINAURAL LISTENING SYSTEM Filed Deo. 23, 1944 latented pr. 25, i950 ELECTROACOUSTIC BINAURAL LISTENING SYSTEM Harold C. Silent, Los Angeles, Calif., assignor to the United States of America as represented by the Secretary of War Application December 23, 1944, Serial No. 569,546

4 Claims.

'l The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

put of the amplifier is connected through an impedance matching transformer I3 to a wire transmission line, which is terminated in an impedance matching transformer Ill connected to a head This invention relates to improvements in 5 receiver I5. electro-acoustic binaural listening systems. One of the channels has variable resistance A binaural listening system of the type herein means l5 for adjusting the feedback voltage fed considered comprises two transmission channels, to the screen of the rst vacuum tube to control each of which is composed of a sound pick-up the gain of that channel. The other channel or microphone, an amplifier, a wire transmission l has a fixed feedback. The output oi both chanline, and a sound reproducer 0r receiver. The nels is controlled simultaneously bya dual potenmicrophones of the two channels are mounted tiometer unit I8 in the grid circuit of the rst together so that their spacing with respect to tube. The amplier output transformer I3, the each other is approximately that of the ears of wire line and the receiver impedance matching a human. The receivers of the two channels are l transformer Ill are phantomed to provide a cirmounted as a pair of head receivers, individually cuit for telephonie communication between the connected to their corresponding channels. If two ends of the line and for remote control of the overall characteristics of the two channels the amplifier ament supply relay from a switch are the same, they will pick up a sound with the at the receivers. same phase, intensity and arrival time relation- By operating a three wafer. three position ship between them as would the human ears and switch, S1, S2, Se to position I, designated baltransmit the sound to the receivers with the same ance on the drawings, the inputs to the two relationships. The system enables the quality, amplifiers are connected in parallel and one-half the approximate direction and the character of of the output voltages of the two ampliers, at sounds to be heard by a person located at some the secondary of their output transformer, are distance from the point at which actual listenconnected together in series with a pair of head ing is desired just as though the person were receivers so that the voltages oppose each other. actually at the listening peint. In such a sys- Under this Condition any sound picked un by the tem, however, besides matching the components microphones will result in Opposing voltages at of the two channels, in order to provide similar the amplifier, and if the gains of the amplifiers transmission characteristics, certain other reare equal, the resultant voltage will be zero. quirements must be met. Therefore, by listening on the head receivers to It is therefore, an object of this invention to a SOurld being DiCked up by the miCrOphOIleS and provi-:le in a binaural listening system, means ior adjusting the gain 0f One amplifier until a minimatching the gains of the two channels to mainmum 0f Sound iS heard, the equality Of gain in tain the proper intensity difference between the the i'fWO Channels iS established. signals in the two Channels. It is desirable that means be provided for deit is a further object to provide, in e binaurai terminins quickly and Without auxiliary equiplistening system, means for poling wire transment that the lines connecting the outpost unit mission lines t0 maintain the proper phase re- 4:0 With ll'ille sOllrld Control unit have been Correctly lationship between the signals in the two poled; that is, that no transposition has been inchannels. troduced in the connection between these units These and other objects are attained by the which would have the effect of reversing the relanovel arrangements and circuits hereinafter detive polarity 0f lCl3riCa1 impulses in the tWO scribed and illustrated in the accompanying channels, as received by the sound control unit drawings, forming a part hereof and in which With respect tC the relative DOlari'y 0f these the figure is a schematic diagram of the electrical transmitted from the Output unil?- circuits and apparatus in accordance with the The DOliug 0f the Wire trallSmiSSlOn line iS invention. accomplished by means of the same wafer switch Referring to the drawings, the binaural listen- 5o and a dOublS-DOIB. dOuble-ihrOW toggle, S4, Ss ing system ig shown t0 comprise two similar switch at the receivers. With the Wafer SWitCh channels, each of which has a listening microin position 2, designated pola and switch S4, phone il, a transformer i2 coupled to a three S5 on position l, designated pole the inputs to stage resistance coupled amplifier with degenerathe two amplifiers are connected in parallel and tive feedback around all three stages. The outthe output voltages of the two receiver imped- 3 ance matching transformers are connected together in series with a pair of head receivers so that the voltages oppose each other when the lines are poled properly. With this connection, providing the amplier gains have been previous- 1y equalized, any sound picked up by the microphones will result in equal and, opposing voltages at the receivers. Therefore, byv listening on the head receivers to a sound being picked up by the microphones and reversing the connections of the two wires of one channel transmissionline, the connection resulting in minimum soundin the receivers is the connection for proper poling of the transmission line.

When the wafer switch S1, Sass, is turned. to position 3, designated listen and the toggle switch S4, S5, is operated to listen thesignals in the two channels are isolated from each other and the system is in condition for binaural: listening.

From theabove description it will be seen that there: has been provided simple effective means for properlyequalizing-Y the gains of amplifiers inthe twoV channels of a binaural listening system.

' The above' description is to be considered as illustrative and; not limitative of the invention, of whichmodications can be made without departing from thescope of the appended claims.

IY claim:

1. In av binauraln listening system having two similar channels, each of saidf; channels having a plurality-stage amplier with degenerative feedback around all' stages, a variable resistance in the feedback path of one of the channels te enable the varying ofthe gainV of thatv channel' without affecting. thev gain of the other channel,

and a dual unit potentiometerl to vary the gain of both channels simultaneously.

2. In a binaural listening system having two similar channels, each of said channels having fiers, attenuator means for equalizing the signal amplificationoft said, channels to maintain the original intensity relation of signals fed into each channel,V and potentiometer means to vary the gain, of the amplifiers in both channels simultaneously.

4. In a binaural listening system having two similar amplifying channels for signal inputs, eachchannel, including-resistive means for varying the gain of that channel without affecting` the gain of the other channel for equalizing the gains of said channels whereby a fixed ratio is maintained between the signals in: each channel, said means comprising a dual unit potentiometer for varying the gain of both channels simultaneously.

HAROLD C. SILENT.

REFERENCES CITED The following references are of record in the file of' this patent:

UNITED STATES PATENTS Number Name Datel 1,946,565 Bauma-n Feb. 23, 1934 2,093,540 Blurnlein Sept. 21, 1937 2,098,561 Beers Nov. 9, 1937 2,126,929 Snow et al Aug. 16, 1938 

